Sulphate-Reducing Bacteria and Their Role in Biocorrosion

Abstract

Sulphate-reducing bacteria (SRB) are the microorganisms most widely implicated in cases of biocorrosion arising in a wide range of natural and industrial environments. Models for their mechanism of action have concentrated on cathodic stimulation of the electrochemical process by hydrogen oxidation and/or the production of iron sulphide corrosion products. Preventatitive measures are largely confined to cathodic protection by sacrificial anode or impressed current, or the use of biocides in contained systems. Although SRB are strictly anaerobic organisms, they can be responsible for extensive biocorrosion under aerobic environmental conditions.

Over recent years two features characteristic of biocorrosion have become domi-nant in our effort to first understand and then control the processes involved.

The physical and chemical nature of the iron sulphide corrosion products and in particular their interaction with oxygen, appear to determine the rate and extent of corrosion.

SRB exist as components of complex microbial communities within a biofilm adherent to the metal surface. This biofilm is a dynamic structure composed of cells, extracellular polymeric substances (EPS), and inorganic inclusions including corrosion products. Many biological and chemical processes become diffusion-limited, and within the biofilm the presence of microenvironments is of great significance to both microbial activities and the electrochemical reactions of corrosion.